Currently, imaging systems are manufactured using one of several different technologies. One of these technologies includes modulating the energy output from a laser light source using an acousto-optic modulator. The modulated laser light is scanned over the image plane, which is fixed to an internal drum, to form the resultant image.
Alternately, the energy output from a laser light source is modulated by an acousto-optic modulator and imaged onto an external rotating drum. The optical head is moved synchronously with the rotation of the drum in the direction parallel to the drum axis.
The above two mentioned technologies can be slightly varied by using a laser diode that is modulated directly rather than via an acousto-optic modulator. All the above disclosed technologies suffer from various limitations. One such limitation is the limit placed on the imaging speed due to the mechanical limitations on the drum or spinner rotation speed.
The imaging speed of an imagesetter is an important factor today in light of resent technological advances in media technology. Many image processes are moving from a film based media to plate based media. The reasons for this are that the new plate technology does not require processing with hazardous chemicals thus eliminating the environmentally unfriendly development process required to process film based media and because a major step in the pre-press process can be eliminated. These new materials, however, require more power per dot for proper exposure, thus increasing the power required for a fixed exposure time.
Many imaging systems today utilize some type of light value or spatial light modulator (SLM) to generate an image onto the media. The majority of the SLM arrays used today are 1-dimensional. In addition, the industry is perpetually striving to reduce the imaging or printing time. The pace that current imaging systems operate at are too slow to achieve these short imaging times. More specifically, the problem lies in the write cycle times of the 1-dimensional SLM arrays used in many of the systems today. These devices are too slow to handle the high data rates needed to achieve such short imaging times.
In addition, SLM arrays based on ferroelectric liquid crystal (FLS)or digital mirror device (DMD) modulators suffer from a limitation in their control of the level of light passing through them since they are bistable devices.
Various schemes for generating and forming an image on a media are taught in the following prior art references. U.S. Pat. No. 4,571,603, issued to Hornbeck et al., teaches an image projection system for producing a projected image in response to electrical signals representing the image to be projected. The electrical signals are transmitted to a light modulator receiving light from an external source. The modulator comprises arrays of deformable mirrors that selectively deflect the light from the external source in response to the electrical signals.
U.S. Pat. No. 5,049,901, issued to Gelbart, teaches a light modulator for imaging a light source onto a two dimensional light valve. The light valve is imaged onto a light sensitive material and the image is scanned along the light sensitive material. The image is input to the first row and transferred to consecutive rows in synch with the movement of the material so that the imaged data is stationary relative to the exposed material.
U.S. Pat. No. 5,309,244, issued to Katagiri et al., teaches an image processing apparatus having a spatial light modulator that is both written to and read from. A laser is moved in two dimensions and illuminates the spatial light modulator. The digital reading and writing system includes a hologram disk having hologram lenses located in a concentric or spiral manner and arranged to deflect the laser beam vertically and horizontally for scanning the spatial modulating element.
U.S. Pat. No. 5,398,082, issued to Henderson et al., teaches a video projection system employing a reflective light value that is optically addressed by an image from a cathode ray tube and provides an output image for projection by means of a high intensity reading light directed to the output face of the liquid crystal light valve. Improved reading illumination is achieved by scanning the face of the liquid crystal light valve with a narrow beam of light that moves across the liquid crystal is synch with the scanning image from the writing cathode ray tube.
U.S. Pat. No. 5,410,370, issued to Janssen, teaches a color projection video system that utilizes a single light valve. A white light source is separated into red, green and blue components. Scanning optics in the form of three prisms cause the RGB bands to be sequentially scanned across a light valve, such as a transmission LCD panel. A particular row is addressed by display electronics with the appropriate color content of that portion of the image which is being displayed, prior to each color passing over a given row of panels on the light valve. The image is then projected by a lens onto a viewing surface, such as a screen.
U.S. Pat. No. 5,416,514, issued to Hanssen et al., teaches a color projection system that utilizes a single light valve. A white light source is separated into red, green and blue components. Scanning optics in the form of three prisms cause the RGB bands to be sequentially scanned across a light valve, such as a transmission LCD panel. A particular row is addressed by display electronics with the appropriate color content of that portion of the image which is being displayed, prior to each color passing over a given row of panels on the light valve. The image is then projected by a lens onto a viewing surface, such as a screen. Also taught is circuitry to synchronize the illumination of the light valve with the video signal and to minimize video breakup when changing video sources.
U.S. Pat. No. 5,428,467, issued to Schmidt, teaches a projection system employing a reflective light valve that is optically addressed by an image from the cathode ray tube and provides an image for projection by means of a high intensity reading light from a lamp. Reading illumination is provided by scanning the face of the liquid crystal light valve with a narrow beam of light that moves across the liquid crystal light valve face in synch with the scanned image from the writing cathode ray tube. The scanned narrow band of illumination is provided by refractive transmission through a rotating transparent polygonal body. Rotation of the polygonal body is synchronized with the vertical sync of the CRT.
U.S. Pat. No. 5,450,219, issued to Gold et al., teaches a telecentric illumination scanning system that comprises an input lens, a rotatable or oscillating reflective scanner, and output lens and a polarizing element. The input lens transmits light from a light source to the scanner, which is then reflected and directed to the output lens. The light transmitted by the output lens is polarized and applied to the light valve. Light is focused into a relatively narrow band of light that is scanned by the rotatable or oscillating scanner across the face of the light valve.
U.S. Pat. No. 5,457,566, issued to Sampsell et al., teaches an optical scanning system comprising a spatial light modulator with minimum diffraction effects that can be scanned by line. Also included is a suitable detector and suitable optics. Applications include infrared and photocopying.
Soviet Union Patent No. 1513519 teaches a device for retrieving data from a movable holographic memory. The device comprises a light beam shaper, a movable array of holograms optically coupled via a restoring lens to a two dimensional spatial light modulator and a multi-element photo-receiver, the output of which is coupled to the input of a data processing unit.